Friction stir spot welding (FSSW) is a solid-state joining process and a rapidly growing dissimilar material welding technology for joining metallic alloys in the automotive industry. Welding tool shape and process conditions must be appropriately controlled to obtain high bonding characteristics. In this study, FSSW is performed on dissimilar materials AA5052-H32 aluminum alloy sheet and SPRC440 steel sheet, and the influence of the shape of joining tool and tool insertion depth during joining is investigated. A new intermetallic compound is produced at the aluminum and steel sheets joint. When the insertion depth of the tool is insufficient, the intermetallic compound between the two sheets did not form uniformly. As the insertion depth increased, the intermetallic compound layer become uniform and continuous. The joint specimen shows higher values of tensile shear load as the diameter and insertion depth of the tool increase. This shows that the uniform formation of the intermetallic compound strengthens the bonding force between the joining specimens and increases the tensile shear load.

The Moving Particle Semi-implicit (MPS) method is one of most famous method in the particle-based computational fluid dynamics field. The MPS, the state-of-art method, is simple but intuitive methodology including multi-phase and complex structure interactions problems. However, the concept of particle method may contain the physical weakness. In order to avoid physical violence, the particle number density and kernel function were employed. Despite all the efforts, the microscopic problems were not easily resolved yet. In this study, the surface tension model was developed and added into the MPS method to strengthen physical phenomena and physics laws. The simulation result with new MPS method including surface tension model was compared with corresponding theoretical results and they show good-agreement.

This study aims at investigating the fracture characteristic according to the shape of the double cantilever beam specimen for mode II with ultra-high strength steel and Mg alloy steel. As the analysis, all three models had the left-hand holes that were constrained by the cylindrical support and the right-hand holes were enforced by the constraint condition of 6mm/min. This study result showed that the shorter the load block of the double envelope test specimen, the higher the safety. The results of this study are thought to be useful for examining the fracture characteristics of specimen for mode II with ultra high strength steel and Mg alloy steel.

Tissue engineering has been rapidly developed in oral and maxillofacial reconstruction. Biocompatible scaffold from chemically composites seeded with stem cells is essential and several growth factors for bone formation and angiogenesis are also required. To overcome limited activity of new bone formation with scaffolds, several biomechanical stimulation methods on cells have been made to grow cells in scaffold. Several bioreactors have been developed for real tissue growth in culture laboratory. In addition to biological stimulants like BMP, growth factors and exogenous drugs, biomechanical stimulation technique has also been known as an effective method in cell differentiation. We developed our own bioreactor with tensile mechanical strains. Then we tested with it for detection of suitable biomechanical effect on the cell differentiation and proliferation. And we also compared the results with the effect of low intensity pulsed ultrasound (LIPUS). Mechanical strain group showed more rapid reaction with cell differentiation and proliferation than non-mechanical strain group. Mechanical strain groups stimulated with 0.5∼0.7Hz for 6 hours and 8 hours showed more active cell differentiation than the group with 0.5∼0.7Hz for 2.5 hours tensile strain stimulation. Group of LIPUS also showed more rapid reaction in cell differentiation and proliferation. LIPUS with 3MHz showed more cell reaction than the LIPUS group with 1MHz. Our results showed the positive effect on differentiation and proliferation of cell with mechanical tensile strain, LIPUS both.

This paper presents the theoretical analysis for the flow driven by surface tension and gravity force in an inclined circular tube. The previously developing equation for Power-Law model is a simple ordinary differential type. A governing equation is developed for describing the displacement of a non-Newtonian fluid(Casson model) that continuously flows into a circular tube by surface tension, which represents a second-order, nonlinear, non-homogeneous, and ordinary differential form. It was found that the theoretical predictions of the governing equation were in good agreement with the results for considering the Newtonian model.

In this paper, the shape adjustment algorithm of the spoked wheel cable structures with retractable membrane system is studied. The initial tension of the membrane or cable is necessary to form the structure and its value is determined by the design shape. However, due to internal and external environmental influences, its shape may be different from the initial designed shape. In the case of the cable structures covered in this study, tension adjustment is necessary to maintain the designed shape because it influences the tension of the cable depending on the state of the retractable membrane. Therefore, we proposed an adjustment algorithm of an initial shape based on the force method. The effectiveness and validity of the methodology were examined through the applicable cable structures. The results of the shape adjustment analysis of the symmetric spoked wheel cable model were reliable and accurate results were obtained.

I형 플레이트 거더는 장경간 구조물, 특히 장경간 교량 및 철도교에 자주 사용되며 리벳 또는 볼트 이음과 같은 방법으로 조립할 수 있고 강판을 용접하여 설계자가 원하는 크기의 거더를 제작할 수 있다. 리벳 또는 볼트를 이용한 연결방식은 시공 중 구조물의 내하력 저하 문제를 피할 수 있고 용접으로 제작된 거더에 비해 유지관리비용이 적다는 장점이 있다. 하지만, 리벳 또는 볼트연결의 경우 하중이 거더에 전달될 때 연결부 주위에 미끄러짐이 발생 할 수 있어 이로 인한 강도감소가 발생할 우려가 있다. 본 연구에서는 유한요소 해석 프로그램을 통해 I형 플레이트 거더의 볼트 이음부의 거동특성을 검토하였다. 또한 수직보강재의 간격이 거더의 강도에 미치는 영향에 대해 검토하였다.

In this paper, we investigated the change of sectional shape according to the tension when the reed wire was rolled. When rolling is performed, the tension acting on the reed wire acts in the opposite direction of the rolling progress and prevents twisting or bending phenomenon. The shape of the cross section was changed according to the tension acting on the reed wire, and the reed wire was rolled by continuously rolling the flat rolled wire and the tension was applied to the reed wire to control the simulation. As a result of the experiment, it was confirmed that the dimensions of the thickness and width after rolling can be adjusted through the tension acting on the lead wire. It was also confirmed that as the tension increased, the length of the lead wire increased and the residual stress increased.

A type of one-way concrete composite slabs made by strain hardening cementitious composites (SHCC) deck combined with high tensile reinforcements was developed and evaluated by four-point slab bending test. The SHCC material was considered to have an high-ductile and strain hardening behavior in tension after cracking. From experimental comparisons with conventional reinforced concrete slab, the proposed SHCC and high tensile reinforced concrete composite slab showed more improved responses both in service and ultimate load capacities as well as in control of crack width and deflection.

Sometimes, it is impossible to install a sensor on a certain location of a structure due to the size of a structure or poor surrounding environments. Even if possible, sensors can be frequently malfunctioned or improperly operated due to lack of adequate maintenance. These kind of problems are solved by the virtual sensing methods in various engineering fields. Virtual sensing technology is a technology that can measure data even though there is no physical sensor. It is expected that this technology can be also applied to the construction field effectively. In this study, a virtual sensing technology based on ARX model is proposed. An ARX model is defined by using the simulated data through a structural analysis rather than by actually measured data. The ARX-based virtual sensing model can be applied to estimate unmeasured response using a transfer function that defines the relationship between two point data. In this study, a simulation and experimental study were carried out to examine the proposed virtual sensing method with a laboratory test on a cable-stayed model bridge. Acceleration measured at a girder is transformed to estimate a cable tension through the ARX model-based virtual sensing.

The fracture of mechanical structure is caused by internal cracks in the material. Particularly, the fracture can also be seen to happen under the stress that is lower than yield strength in case of high strength steel because of the crack happening from the defect inside the material. In this study, high strength steel with four holes near the center crack were designed by angle and fatigue experiments, and the simulation analyses to verify the experimental results were carried out. As the results of this study, the crack growth rates are shown to be 0.000485, 0.000434 and 0.000422 respectively at the inclined angles of center crack as 22.5°, 45° and 67.5°. The maximum deformation energies become 0.0848mJ, 0.0603mJ and 0.0582mJ respectively at the inclined angles of center crack as 22.5°, 45° and 67.5°. It is thought that this study result can be utilized as the basic data at the study on the material existing with the defects of crack and hole.

Corrosion is one of the most typical aging phenomena associated with long-term use of steel structures. Corrosion of high-tension bolted connections causes problems such as reduction of thickness of member and relaxation of axial force of high-tension bolt, thereby reducing load-carrying capacity of high-tension bolted connections. In this study, three specimens were subjected to natural corrosion in order to evaluate the residual load-carrying capacity of high-tension bolted connections where corrosion occurred. Two specimens were newly fabricated for comparison with the corroded specimens. In addition, the static bending test was performed to compare and investigate the behavior characteristics of the high-tension bolted connections and the final failure modes. The residual load-carrying capacity of the corroded high-tension bolted connections was evaluated.

This study aims to reduce the force exerted to the buoy of the gillnet by wave and current. Five buoy models were selected for experiments and their rope tensions under wave and current action were compared. Five models were EL (ellipsoid), EL-H (ellipsoid-hole), SL (streamlined body), SP (sphere) and CL (cylinder, traditional type). In the first experiment, the Five models were tested without any attachment. In the second experiment, a flagpole was attached to each model. As a result, in the condition without flagpole, the tensions of four models with the exception of the CL were about a half of that of the CL. In the condition with flagpole, the tension of all models was twice larger than that without flagpole. Thus, a new model was suggested to improve the problem, which has a combined body that of a flagpole and a buoy Three new models of CL-L (long and thin cylinder), LF (leaf shape) and LF-F (leaf shape with fin) were designed. Also a cylinder type (CLD) with a flagpole as a control was included in the experiment. As a result, the LF-F had the smallest tension and a half tension of the CLD. Therefore, it is supposed that the flagpole and buoy combined model could reduce the tension on buoy rope and contribute to improve the gillnet loss problem.

Measuring the exact cable tension force is important to cable supported bridge under construction and on service. This study was planned to propose EM(electro-magnetic) sensor-based method for measuring the tension force of MS(multi-strand) cable in cable-stayed and extradosed bridge. The tension force in each strand is the same due to MS cable construction using Iso-tensioning system. Therefore, In this prosed method, EM sensor was installed directly at a strand and the measurement model was established for estimating the tension force of strand via EM sensor by experiments. The measurement model was derived from the relation of tension force and magnetic permeability. Also, the magnetic permeability is shown to be different according to the magnetization characteristic of 1860MPa and 2200MPa high-strength strand. The difference is increased as tension force increases. Additional experiment was conducted to verify the measurement model. As a result, the distribution of strand tension calculated upon the EM sensor is similar to those of tension measured by load cell. This proposed approach can be an effective tool for monitoring and measuring the cable force of MS cable.

Behavior of RC(Reinforced-concrete) beam-column connections has been subjected to the earthquake loading has been determined by shear and attachment mechanism. However, since the shear and attachment are very fragile for cycle loadings. Through occurring plastic hinges at the beam, the column and the connection should remain elastic condition and the beam should dissipate the energy from the earthquake. This study was investigate on the seismic performance of 6 RC beam - column connections built with the high strength reinforcements (700MPa) based on design and detailing requirements in the ACI 318-05 Provision and KCI-07 appendix Ⅱ. This is aimed to evaluate the effect of the high-strength reinforcements as used the beam-column connection members. The main comparisons were the seismic performance of the connections affect the seismic performance in terms of strength, stiffness and ductility, joint shear stress-strain. A total of 6 beam-column specimens were built with a 1/2 scale and subjected to the cyclic loadings. Main design considerations were the area of the longitudinal reinforcements of the beam and details of the beam-column joint designed based on the seismic code. Cyclic test results are given and recommendations for the usage of high strength reinforcements for the seismic design is provided.

Membrane structure is a system that is stabilized by maintaining a tensile state of the membrane material that originally cannot resist the bending or pressure. Also, it is a system that allows the whole membrane structure to bear external loads caused by wind or precipitation such as snow, rain and etc. Tension relaxation phenomenon can transpire to the tension that is introduced to the fabric over time, due to the innate characteristics of the membrane material. Thus, it is important to accurately understand the size of the membrane tension after the completion of the structures, for maintenance and management purposes. The authors have proposed the principle of theoretically and indirectly measuring the tension by vibrating the membrane surface with sound waves exposures against the surface, which is compartmentalized by a rectangular boundary, and by measuring the natural frequency of the membrane surface that selectively resonates. The authors of this paper measured the tension of preexisting membrane structure for its maintenance by using the developed portable measurement equipment. Through analyzing the measurement data, the authors review the points that should be improved and the technical method for the new maintenance system of membrane tension.